The invention relates generally to a method and apparatus for setting the position of objects relative to a datum plane, the method and apparatus finding particular utility in setting anodes in an electrolytic cell, though the invention is not limited thereto.
In processes that involve the consumption of elements, the elements are usually inserted or installed in apparatus of the process in a manner that provides a uniform setting of the elements. Without such uniform setting, the process functions inefficiently if it functions at all. An example of this is the setting of carbon anodes in a Hall reduction cell relative to a molten aluminum pad located in the lower cathode bottom of the cell. The carbon material of the anodes burns off at a substantially uniform rate, but the anodes in any given cell are not placed in the cell at the same time. As the anodes burn off, they are lowered toward the aluminum pad to maintain a proper predetermined distance between the bottom surface of the anode and the datum plane of the pad. At the completion of the burn off process, a new, full size anode is put into place in place of the burned off anode, the new anode often being placed beside an anode that is partially consumed. In the process of locating the new full size anode in the cell, the anode is lowered in the cell by a supporting rod until the bottom surface of the anode is located above the metal pad in the same horizontal plane as the bottom surfaces of the other anodes in the cell including partially consumed anodes.
Heretofore, anode setting has been based largely on the horizontal position of bridge structures that support the anodes in the cell, the bridge structures being located over the cell and extending along the length of the cell. Because of the heat rising from the cell and the weight of the anodes suspended from the bridge, the bridge can sag as much as 11/4 inches adjacent the center portion thereof such that the bridge is not itself a good horizontal reference for setting anodes.
What is needed in the industry is a method and means that can provide a horizontal reference independent of supporting bridge structures such that a consistently reliable reproducible reference is available for anode setting. In addition, the means should be simple and inexpensive to use.